Rescued from under a pile of damaged aeroplanes at the back of an old hangar, a piece of New Zealand's agricultural aviation history is slowly being restored to its former glory.

The Hupmobile 1924 sedan car, converted to a truck with loading gear built on top, was first used on May 21, 1949, to load the first Tiger Moth used for topdressing.

It attracted huge interest recently when it was put on on display at the Central Districts Field Days in Feilding.

Owner and pilot, Hallett Griffin, said although he also had one of his Grumman Ag-Cat spraying airplanes on display, people were more interested in the Hupmobile.

"Back in the 1920s, when the Hupmobile was released, most of them went to South Island owners. I had never heard of any in the North Island, but during the field days three Manawatu people told me their grandfathers had one, which is very unusual but fascinating."

Mr Griffin said he had seen pictures of the converted Hupmobile, which piqued his curiosity as to what had become of the machine. So began a search lasting several years.

"Considering its age, the Hupmobile wasn't in too bad a condition, although it was rusty and had a few dents here and there."

Griffin Ag-Air employee Alex Kaandorp spent many hours pulling the Hupmobile apart - and putting it back together - as the two men slowly and painstakingly began restoring the machine to its former glory.

"The bodywork has been panelbeaten and repainted, and we have had new wheels and hubs put on.

"It is a winter project but we will continue restoring it as time allows," Mr Griffin said.

The engine is being rebuilt and the wooden cab, which no longer exists, will also have to be rebuilt. There are also plans to rebuild the loading gear, which originally consisted of one and a half 44 gallon drums.

"We hope to have a lot of the work done in time for it to be a showpiece at the 2015 Central District Field Days.

"The Hupmobile attracted a great deal of interest and was a great way to promote the agricultural aviation industry to the public and help them realise it is an important contributor to the New Zealand economy."

Alongside New Zealand's oldest topdressing loader was also the newest, the Grumman Ag-Cat, which provided a stark contrast to the Hupmobile.

"When the Hupmobile was built, no-one would have believed we would be using machines like the Grumman now. It has 10 times the capacity of the Hupmobile, which can hold 200kg, which means topdressing planes today are also spreading 10 times what the old Tiger Moths used to do," Mr Griffin said.

The Hupmobile will become a showpiece in Mr Griffin's private agricultural aviation museum.

The museum already features a 62-year-old Beaver Fieldair plane, which rolled off the De Havilland production line in Canada in 1951. The plane was shipped to New Zealand and put into service as an aerial topdresser, becoming a familiar sight over Dannevirke, Gisborne, Wairoa, Dannevirke and Masterton. A Percival EP9, a Transland Ag2 Ag-2, a Zlin from Czechoslovakia and a 1929 Travelair 4000 also feature.

Mr Griffin also has a pink 2002 Cresco agricultural spreader, which he acquired in 2009.

The plane was pink when he bought it, and he had intended to paint it in the company colours. But he decided to leave it pink as a way of acknowledging the extensive contribution women make to New Zealand farming, and to agricultural aviation.